284 MICROBES, FERMENTS, AND MOULDS. 
microbe subsists in the blood, the inner part of the 
organs, or merely on the surface of the digestive canal. 
Such are the microbes of anthrax, of tuberculosis, and 
of cholera, natural diseases which are not produced by 
the experiments of man. Up to this time a septic 
microbe has not been proved to be transformed into a 
truly pathogenic microbe, and consequently a com- 
pletely new disease, characterized by the development 
of this microbe in the body of man or animals, has 
not been created. 
It must also be remarked—and this peculiarity is 
common to both classes of microbes—that certain 
bacteria produce very different effects, according to 
the animals into whose bodies they are introduced. 
Thus guinea-pigs cannot be inoculated with the 
experimental septicemia of rabbits and mice; and 
dogs and swine display more or less resistance to the 
inoculation of anthrax. Finally, there are cases in 
which the attempt to inoculate an animal with a 
contagious disease merely produces a septicemia 
which must not be confounded with it. This result 
will not astonish those who know that some species 
of plants, poisonous to man, can be eaten with im- 
punity by many animals. But it is well to keep 
this fact in mind in laboratories, when’ the attempt 
is made to inoculate animals of various species, 
